Color changing EL wire

All EL wire drivers use a resonator circuit to supply power to the EL wire. It’s an efficient system, but [Paul] noticed that there was some color change when powering different lengths of wire off of the same driver. He realized that this is because of the changing frequency of the resonator circuit, so the only reasonable thing for [Paul] to do was to build a color fading EL wire driver.

The circuit used to drive the wire is very simple. [Paul] used a Teensy board to switch two transistors and produce AC current. This is sent through a step-up transformer which powers the EL wire. It was necessary to use aqua or ‘Tron blue’ EL wire for this build because of the clear wire jacket. Many colors of EL wire have a fluorescent jacket – much like a fluorescent light bulb – that changes the color produced inside the wire to something different. [Paul] says the color change is subtle, but unique.

Of course the build is nothing without a video of the color changing EL wire. Check it out after the break.

Very cool Brian.. But have you played much with driving it with a analog source (or analog-looking source).. and played with MIXING the frequencies? Doing so could get you more variance and color combinations (one would think).

@dcroy – Opps, I didn’t know about your project. You definitely built this first!! I’ve updated my page with a link to your blog. You clearly deserve the credit.

@Headshot-Zombie – Is using a $16 board that’s extremely easy to change in almost any way, rather than cheaper analog circuitry that requires soldering to change in substantial ways, considered a “big fail”? I can see that for production of thousands, or hundreds, or even a dozen units. But the very first prototype, even before the frequency ranges and other parameters are known? I built and tested this whole thing in about half a day, and being able to quickly download different programs (I tried a LOT of different ways) and tweak the delays saved a lot of time.

awesome that you took the time to figure this out. though i am sure you can achieve a greater number of steps. i have el gauges installed in my car that do this with about 6 steps of green-blue. though i am not sure of the differences between el paper and el wire.

@Headshot-Zombie standard high frequency ac drivers (for el wire, ccfl tubes, neon) typically use a plain square wave to pulse drive a step up transformer to generate ac, using a digital signal source adds the flexibility of being programmable

ill be working on an a pic driven version of my own driver to play with some mixed frequency driving to try and solve the problem with driving electroluminescent at higher frequencies (brighter, with the bonus color shift but considerably lower lifespan)

something along the lines of modulating between two frequencies to increase brightness while mitigating the reduction in lifespan

I ran into the problem of driving an EL display a few months ago when I bought some EL backlight LCD displays. The problem is getting the frequency and voltage correct. My displays want 111VAC @ 120Khz which is a pain to generate cheaply. Now I know why the guy sold them to me so cheap :)

I don’t see much in the way of colour change either. It’s there, but very subtle. I’m also somewhat colour-blind. A great many people, especially men, are somewhat colour-blind and don’t even know it. Maybe that is the issue in your case?

Despite what all the naysayers of digital tech say, having an AVR for prototyping purposes is extremely useful. I doubt any of the analog purists would enjoy building a custom-designed circuit just to find out that it wouldn’t work with the particular strand of EL wire. Digital tech allows prototypes to be made very rapidly, and once [Paul] figured out what the frequency(ies) were, I’m sure it would be loads easier to wire up a circuit using discreet components.

@cgimark I have used the Supertex chips and they work very well indeed.
One caveat, its worth adding a series 150 ohm in each lead because they *really* hate phase-phase shorts.
Effect on brightness is minimal and the chip will last forever this way even if the EL goes S/C.

Did I mention that these chips also have frequency shifting “out of the box” by altering the timing resistor?

About the most innovative use I have come up with is hacking the HV809 to drive a resonant flapper setup for the purpose of driving a model ornithopter. The problem was that I ran out of time not that anything broke, the hardware was perfect.

i have a el inverter i bought at a surplus store
i noticed the effect that when i have it stuck to a stack of magnets(roughly 20 microwave oven magnets)
the frequency changed(you could clearly hear it going atleast 500 hz higher) and so did the color
became whiter and less blue

@Missy McGavin – Sparkfun carry a flexible light guide a bit like a fibre optic pipe, it has its own problems, but it still looks mighty cool.

@Paul – I had heard about this colour changing property but like you I struggled to find any details. Having seen the effect I must say I really like the subtle shift; I may incorporate this in a night light I’m working on.

Another way of subtly shifting the colour is to introduce UV light to EL wire without the colour filter layer. The pigment fluoresces in a white/green colour when off, and pulls the colour slightly towards the green end when the EL wire is powered.

I like this; I’m trying to get something similar together using an Arduino, but I’m finding it hard to work out what parts to get (specifically the transformer – I’m hoping I can find one suitable at uk.farnell.com )

Also, it looks from the 555 version that it ought to be possible to do this using only one pin on the arduino – is that right?

Yeah, that Mouser 42TU003-RC looks like a part Mouser has made. Will Mouser ship to Europe?

If you use only 1 transistor, you’ll probably end up driving the transformer with a DC bias. Well, unless you put a large DC blocking capacitor in series with the winding. Putting an DC on a coil causes a lot of extra magnetic field in the core which doesn’t help, so you’ll need a bigger transformer.

That’s why I used 2 transistors with a center tap winding. As long as you alternately switch each transistor on for the same length of time, you’ll avoid any DC bias.

Also, you might trying Arduino 1.0 instead of 0022. 1.0-beta3 was released yesterday. Apparently 1.0 is scheduled for Sept 15. Here’s the beta.

One of the improvements is optimization of digitalWrite if you use constants for both inputs. Teensyduino has had this for almost 2 years (and I’ve tried to contribute it into the official Arduino since November 2009) and finally it’s in 1.0. If you’re reading this after Sept 15, hopefully 1.0 will be officially released. The betas seem to be working ok, and for this project the optimized digitalWrite is definitely worth using the beta test version.

They will ship to Europe, for a price, but I’d prefer to avoid that cost if I can; everything else I can source locally!

So I’m basically looking for a transformer with the same number of turns on each side, but on one side there’s a central tap? And presumably I might need to alter the values of the capacitor/resistor network if I can’t get equivalent coil resistance? How did you determine those values?

If I did want to go down the single pin route, when you say a “large” blocking capacitor, how large is this? And does it need to be OK for reverse voltages? I think from what I’ve read that the reason the single transistor version works is because you get an instantaneous high negative voltage on the transistor’s collector?

(Sorry if these are silly questions, still relatively new to this)

Thanks for the tip on the new arduino software – I’m actually using a slightly different board from jeelabs.net but it’s easier to say “arduino” than to go into details; I need the various support libraries he provides, so I’ll wait until he’s confirmed they all work before switching over.